1. Field of the Invention
The invention relates to a method for manufacturing a hollow molded article having a layer of ethylene/xcex1-olefin copolymer and containers obtained by such method. More specifically, it relates to a method for manufacturing a hollow molded article having improved extrudability and mechanical strength and containers obtained by such method.
2. Description of the Background
Containers manufactured by the blow-molding method are used for various applications. For example, such containers comprising a single layer are used as food, kerosene and other containers; such containers comprising multiple layers with an ethylene/vinyl alcohol copolymer or polyamide resin are used as soft blow-molded containers such as mayonnaise and ketchup containers to keep the flavor of food; such containers in the form of blow-molded tubes are used as wasabi Japanese horseradish paste or mustard paste containers; and such containers in combination with corrugated board boxes, steel cans, etc. are used as back-in-boxes, drum-inner-bags, etc. Polyethylene is widely used for the raw material of these containers, and particularly a linear low density polyethylene (L-LDPE) is mainly used in the areas requiring heat resistance and mechanical strength.
However, the linear low density polyethylene tends to cause its parison to suffer a drawdown at the time of extrusion because of its low melt tension. On account of this, the linear low density polyethylene is not only difficult to mold but also hollow molded articles manufactured therefrom show a deviation in their wall thickness, thereby causing a decline in their mechanical strength. If a formulation in which a high-pressure low density polyethylene is blended to the linear low density polyethylene is adopted to improve such problem, the melt tension will increase, but the strength, for example, drop impact strength of a hollow molded article thereof may decline in some cases because the high-pressure low density polyethylene itself does not always have high mechanical strength.
Further, conventional linear low density polyethylene resins, having been manufactured by use of a titanium polymerization catalyst, have a broad molecular weight distribution and consequently contain a low molecular weight matter intrinsically. Because of this, there is a concern that such low molecular weight matter may be dissolved into the contents of hollow molded articles made of such conventional linear low density polyethylene resins. In this respect, new polyethylene resins manufactured by use of a metallocene polymerization catalyst have the characteristic of having a relatively narrow molecular weight distribution and composition or component distribution, and there is little concern that such polyethylene resins will cause the problem of any low molecular weight matter dissolving into the contents of hollow molded articles made thereof. However, it is said that with even such polyethylene resin yet having low melt tension, the manufacture of hollow molded articles is difficult similarly.
Accordingly it is an object of the invention to provide a method for manufacturing a hollow molded article showing an improved drawdown characteristic of a parison.
Another object of the invention is to provide a method for manufacturing a hollow molded article showing high mechanical strength and a small amount of extraction of its material into the contents of the hollow molded article.
Further object of the invention is to provide a container obtained by the method.
Other and further objects, features and advantages of the invention will appear more fully from the following description.
The present invention is related to a method for manufacturing a hollow molded article, in which at a time of blow-molding a parison having at least one ethylene/xcex1-olefin copolymer layer by extruding it through an extruder die:
(1) the copolymer meets following physical properties (a) to (e):
(a) a density (d) is 0.880 to 0.970 (g/cm3);
(b) a melt flow rate (MFR) is 0.01 to 10 (g/10 minutes);
(c) a relationship between a melt tension (MT (g)) at 190xc2x0 C. and the melt flow rate (MFR (g/10 minutes)) is:
MT greater than 2.2xc3x97MFRxe2x88x920.84;
(d) a relationship between a decane soluble matter content (W (wt %)) at 23xc2x0 C. and the density (d) is:
W less than 80xc3x97exp{xe2x88x92100(dxe2x88x920.88)}+0.1;
xe2x80x83and
(e) a relationship between a temperature (Tm (xc2x0 C.)) at a position of the highest peak of an endothermic curve as measured by use of a differential scanning calorimeter (DSC) and the density (d) is:
Tm less than 400xc3x97dxe2x88x92248,
xe2x80x83and
(2) a resin pressure P (kg/cm2) at a time of extruding the parison has following relations with a resin temperature T (xc2x0 C.), an extrusion rate K (kg/hour), an extruder die lip cross-section area A (cm2) and the melt flow rate MFR (g/10 minutes) of the resin.
15033 {K/(MFR)1.5/(Txe2x88x92120)/A}0.2xe2x89xa6Pxe2x89xa6500xc3x97{k/(MFR)1.5/(Txe2x88x92120)/A}0.2.
The present invention is also related to a container manufactured by the method, and it may be either single-layer container or multi-layer container.
The hollow molded article manufacturing method of the invention relates to a method for manufacturing a hollow molded article having an ethylene/xcex1-olefin copolymer layer. Next is given a specific explanation of each constituent of the manufacturing method and containers obtained by the method.
The material of such hollow molded article is a random copolymer of an ethylene and an xcex1-olefin. As such xcex1-olefin, an xcex1-olefin having 3 to 20 carbon atoms is preferable. Specific examples of the xcex1-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene and 1-dodecene.
The ethylene content of the copolymer is normally 94 to 99 mol %, preferably 96 to 98 mol %, and the comonomer xcex1-olefin content is normally 1 to 6 mol %, preferably 2 to 4 mol %. The ethylene and xcex1-olefin contents can be measured by use of 13C-NMR.
Specifically, the composition of the copolymer can be determined normally by measuring 13C-NMR spectrum of a sample obtained by dissolving approximately 200 mg of the copolymer uniformly in 1 ml of hexachlorobutadiene in a test tube 10 mmxcfx86 under the conditions of the test temperature of 120xc2x0 C., test frequency of 25.05 MHz, spectrum width of 1500 Hz, pulse repeating time of 4.2 seconds and pulse width of 6 xcexcsec.
The density of the copolymer is in the range of 0.880 to 0.970, preferably 0.890 to 0.940 (g/cm3). If the density is in this range, it is desirable that a hollow molded article having excellent low-temperature impact resistance, rigidity and chemical resistance may be obtained. Here, the density is measured at 23xc2x10.1xc2x0 C. in accordance with Method D of JIS K-7112.
Moreover, the value of the MFR of the copolymer as measured at 190xc2x0 C. and under a load of 2.16 kg in accordance with ASTM D-1238 is 0.01 to 10, preferably 0.05 to 9 (g/10 minutes). It is preferable that the MFR should be in this range because a hollow molded article having a satisfactory appearance may be obtained at high molding speed.
In addition, it is desirable that the copolymer should show the following relationship between melt tension (MT (g)) at 190xc2x0 C. and melt flow rate (MFR (g/10 minutes)):
MT greater than 2.2xc3x97MFRxe2x88x92084,
preferably,
MT greater than 4.0xc3x97MFRxe2x88x920.84.
If the melt tension is in this range, the drawdown characteristic of the parison is improved, and the mechanical strength of the hollow molded article is increased.
Here, the melt tension is determined by measuring the stress of a melted polymer when it is stretched at a constant rate. Specifically, resin pellets are fed to a melt tension tester, available from Toyo Seiki Seisakusho, and the melt tension is measured under the conditions of resin temperature: 190xc2x0 C., extrusion rate: 15 mm/min., take-up speed: 10 to 20 m/min., nozzle diameter: 2.09 mmxcfx86, and nozzle length: 8 mm.
On the other hand, it is desirable that the copolymer should show a relationship between the decane soluble matter content (W (wt %)) at 23xc2x0 C. and the density (d) which meets the following conditions:
W less than 80xc3x97exp{xe2x88x92100(dxe2x88x920.88)}+0.1,
preferably,
W less than 60xc3x97exp {xe2x88x92100(dxe2x88x920.88)}+0.1.
If the relationship between W and d is as shown above, that implies that the copolymer has a low content of low-molecular-weight matter. This may make it possible to reduce the amount of such low molecular weight matter bleeding out onto the wall surface of the hollow molded article, and to lessen the stickiness of the surface of the hollow molded article, which phenomenon was experienced with conventional linear low density polyethylene resins.
The decane soluble matter content (W) was measured by the method as described below. Approximately 3 g of the sample were added to 450 ml of n-decane and dissolved at 145xc2x0 C. After that, the liquid was cooled to 23xc2x0 C. and filtered for the removal of the n-decane insoluble matter. The n-decane soluble matter was recovered from the filtrate. The soluble and insoluble matter contents were measured by performing these operations, and the W value was calculated by the following formula:
W={(n-decane soluble matter content)/(n-decane soluble matter content+insoluble matter content)}xc3x97100 (wt %)
In addition, the copolymer shows the following relationship between the temperature (Tm (xc2x0 C.)) at the position of the highest peak of the endothermic curve as measured by use of a differential scanning calorimeter (DSC) and the density (d):
Tm less than 400xc3x97dxe2x88x92248,
preferably,
Tm less than 450xc3x97dxe2x88x92297.
The relationship between Tm and d as shown above implies that the copolymer shows a narrow composition distribution of the ethylene and the xcex1-olefin, and is desirable because the hollow molded article will have improved mechanical strength.
Here, in measuring the temperature at the highest peak position by use of DSC, Model DSC-7, available from Parkin Elmer, was used. Specifically, approximately 5 mg of the sample were packed into an aluminum pan and heated to 200xc2x0 C. at a rate of 10xc2x0 C./minute. When the temperature reached to 200xc2x0 C., it was kept at that level for 5 minutes, lowered to room temperature at a rate of 10xc2x0 C./minute and raised again at a rate of 10xc2x0 C./minute, and the endothermic curve was obtained. The temperature corresponding to the highest peak was determined from the endothermic curve.
Further, the ethylene/xcex1-olefin copolymer may be a copolymer having at least not less than one peak in the endothermic curve as determined by DSC in addition to the aforesaid highest peak. As shown in the Examples as described below, a copolymer having two or three peaks in the vicinity of 105xc2x0 C., 113xc2x0 C. and 123xc2x0 C. as well as a copolymer having one peak may be used for the ethylene/xcex1-olefin copolymer.
The ethylene/xcex1-olefin copolymer meeting the aforesaid physical properties (a) through (e) is a material for a hollow molded article having excellent mechanical strength and showing satisfactory extrudability and blow-moldability, and it is suitable for use in the manufacture of hollow molded article.
Furthermore, it is desirable that the copolymer should contain a matter which is not extracted below 100xc2x0 C. in a Temperature Rising Elution Fraction Test (TREF) and the amount of such matter is not more than 10 wt %, preferably not more than 8 wt %. If the insoluble matter content is within such range, the amount of the hollow molded article material bleeding out into the contents of the hollow molded article is little; and therefore such hollow molded article is preferable from a viewpoint of reducing the amount of the molded article material bleeding out into the contents of the molded article when the hot-filling of the contents is performed. The conventional linear low density polyethylene resins produced by use of a titanium polymerization catalyst contain a large amount of such insoluble matter as determined by the Temperature Rising Elution Fraction Test as shown in the Comparative Examples as described below, and therefore it is assumed that this has something to do with the extraction phenomenon caused by the bleeding-out of such insoluble matter into the contents of the molded article.
The Temperature Rising Elution Fraction Test (TREF) was conducted as follows.: The copolymer was dissolved in o-dichlorobenzene at a concentration of 200 mg/40 ml. 7.5 ml of the solution were injected into a column (2.14 cmxcfx86xc3x9715 cm) filled with glass beads (100 xcexcmxcfx86) and cooled to 25xc2x0 C. at a temperature falling rate of 10xc2x0 C./hr. After that, while the temperature was being raised at a temperature raising rate of 15xc2x0 C./hr, o-dichlorobenzene was supplied continuously at a constant rate of 1.0 ml/min. The matter being extracted was detected on line, and as a result, an extraction curve was drawn.
Moreover, it is desirable that in the molecules of the copolymer, there are more than three long-chain branches having not less than 6 carbon atoms per 1,000 carbon atoms as determined by NMR measurement. If the copolymer molecules have many long chains as described above, the melt tension will be raised, the drawdown characteristic of the parison will be improved, and the extrudability will be better. By contrast, conventional linear low density polyethylene resins have a small number of long chains, and this is presumed to be one of the reasons for them to tend to suffer a drawdown of the parison.
Furthermore, it is desirable that the copolymer should show a weight-average molecular weight (Mw)/a number-average molecular weight (Mn) ratio, i.e. Mw/Mn, being in the range of 2.8 to 15, preferably 3.0 to 10. If the Mw/Mn value being a broad or narrow index of molecular weight distribution is in this range, the copolymer shows a relatively narrow molecular weight distribution, and yet has a low content of low-molecular-weight polymer. Because of this, it may be possible to make the hollow molded article surface unsticky and reduce the amount of the material bleeding into the contents of the hollow molded article.
Further, the Mw/Mn value was obtained by measuring the Mw and Mn values of the copolymer by use of GPC and calculating the ratio between them. The GPC was conducted at 140xc2x0 C. by using GPC Model ALC-GPC-150C available from Waters Co., using PSK-GMH-HT available from Tosoh Corporation as the column and the o-dichlorobenzene as the solvent.
Further, additives such as antioxidants, weathering stabilizers, light stabilizers, heat stabilizers, antistatic agents, lubricants, pigments, dyes, nucleators, plasticizers and hydrochloric acid absorbers may be compounded to the ethylene/xcex1-olefin copolymer as required to such extent that the purpose of the invention is not frustrated. The ethylene/xcex1-olefin copolymer, which is blended with such kind of additives as required, is preferably used for blow molding after it is mixed by use of a mixer such as a Henschel mixer, a tumbling mixer, a ribbon mixer, a Banbury mixer, a single-screw extruder, and a twin-screw extruder.
The copolymer having the physical properties can be manufactured satisfactorily by feeding an ethylene and an xcex1-olefin having 3 to 20 carbon atoms to the polymerization system, using the olefin polymerization catalyst components (a) to (d) as described below.
(a) a transition metal compound in the Group IV of the periodic table which contains a ligand having the cyclopentadienyl skeleton;
(b) an organoaluminium oxy-compound;
(c) a support; and
(d) an organoaluminium compound as required.
First given below an explanation of the olefin polymerization catalyst.
 less than (a) Transition Metal Compound greater than 
This compound forming the center of the catalyst system is a transition metal compound in the Group IV of the periodic table containing a ligand having the cyclopentadienyl skeleton and is represented by the following general formula:
M L1(x)xe2x80x83xe2x80x83(I)
(In the formula,
M represents a transition metal selected from the Group IV of the periodic table, specifically zirconium, titanium or hafnium, preferably zirconium;
L1 represents the ligands attached to the transition metal atom, out of which at least two ligands L1 are the cyclopentadienyl group or the substituted cyclopentadienyl group having not less than one substituent selected from among the hydrocarbon groups having 2 to 10 carbon atoms, with the other ligands being the hydrocarbon group having 1 to 12 carbon atoms, alkoxy group, aryloxy group, halogen atom, trialkylsilyl group or hydrogen atom, and each ligand and substituent may be the same or different from one another; and
x represents the valence of the transition metal atom M.)
Examples of the transition metal compound represented by the above general formula include such compounds as:
Bis(cyclopentadienyl)zirconiumdichloride,
Bis(methylcyclopentadienyl)zirconiumdichloride,
Bis(ethylcyclopentadienyl)zirconiumdichloride,
Bis(n-propylcyclopentadienyl)zirconiumdichloride,
Bis(n-butylcyclopentadienyl)zirconiumdichloride,
Bis(n-hexylcyclopentadienyl)zirconiumdichloride,
Bis(n-hexylcyclopentadienyl)zirconiumdichloride,
Bis(methyl-n-propylcyclopentadienyl)zirconiumdichloride,
Bis(methyl-n-butylcyclopentadienyl)zirconiumdichloride,
Bis(dimethyl-n-butylcyclopentadienyl)zirconiumdichloride,
Bis(n-butylcyclopentadienyl)zirconiumdibromide,
Bis(n-butylcyclopentadienyl)zirconiummethoxychloride,
Bis(n-butylcyclopentadienyl)zirconiumethoxychloride,
Bis(n-butylcyclopentadienyl)zirconiumbutoxychloride,
Bis(n-butylcyclopentadienyl)zirconiumethochloride,
Bis(n-butylcyclopentadienyl)zirconiumethylide,
Bis(n-butylcyclopentadienyl)zirconiumbenzylchloride,
Bis(n-butylcyclopentadienyl)zirconiumdibenzyl,
Bis(n-butylcyclopentadienyl)zirconiumphenylchloride,
Bis(n-butylcyclopentadienyl)zirconiumhydridechloride,
Bis(dimethylcyclopentadienyl)zirconiumdichloride,
Bis(diethylcyclopentadienyl)zirconiumdichloride,
Bis(methylethylcyclopentadienyl)zirconiumdichloride,
Bis(dimethylethylcyclopentadienyl)zirconiumdichloride,
Bis(dimethylcyclopentadienyl)zirconiumdibromide,
Bis(dimethylcyclopentadienyl)zirconiummethoxychloride,
Bis(dimethylcyclopentadienyl)zirconiumethoxychloride,
Bis(dimethylcyclopentadienyl)zirconiumbutoxychloride,
Bis(dimethylcyclopentadienyl)zirconiumdiethoxide,
Bis(dimethylcyclopentadienyl)zirconiummethylchloride,
Bis(dimethylcyclopentadienyl)zirconiumdimethyl,
Bis(dimethylcyclopentadienyl)zirconiumbenzylchloride,
Bis(dimethylcyclopentadienyl)zirconiumbenzyl,
Bis(dimethylcyclopentadienyl)zirconiumphenylchloride, and
Bis(dimethylcyclopentadienyl)zirconiumhydridechloride.
In the examples, the two substituents of the cyclopentadienyl ring contains 1,2-and 1,3-substituents, and the three substituents contain 1,2,3-and 1,2,4-substituents. Further, in the zirconium compounds, a transition metal compound replacing the zirconium metal with titanium metal or hafnium metal may be used.
Out of the transition metal compounds represented by the general formula, the following compounds are preferable:
Bis(n-propylcyclopentadienyl)zirconiumdichloride,
Bis(n-butylcyclopentadienyl)zirconiumdichloride,
Bis(1-methyl-3-n-propylcyclopentadienyl)zirconiumdichloride,
Bis(1-methyl-3-n-butylcyclopentadienyl)zirconiumdichloride,
Bis(1,3-dimethylcyclopentadienyl)zirconiumdichloride,
Bis(1,3-diethylcyclopentadienyl)zirconiumdichloride, and
Bis(1-methy-3-ethylcyclopentadienyl)zirconiumdichloride.
The transition metal compound used may be a mixture of two or more of the transition metal compounds represented by the aforesaid general formula. Specifically, examples of such mixture include the following combinations:
A combination of bis(1,3-n-butylmethylcyclopentadienyl)zirconiumdichloride and bis(1,3-dimethylcyclopentadienyl)zirconiumdichloride;
A combination of bis(1,3-n-propylmethylcyclopentadienyl)zirconium-dichloride and bis(1,3-dimethylcyclopentadienyl)zirconiumdichloride; and
A combination of bis(n-butylcyclopentadienyl)zirconiumdichloride and bis(1,3-dimethylcyclopentadienyl)zirconiumdichloride.
Further the transition metal compound may be a mixture of a transition metal compound represented by the aforesaid general formula (I) and a transition metal compound represented by the following general formula (II):
M K L2(xxe2x88x922)xe2x80x83xe2x80x83(II)
(In the formula,
M represents a transition metal selected from the same Group IV of the periodic table as described above;
K and L2 represent the ligands attached to the transition metal atoms, with the ligand K being the same or different indenyl group, substituting indenyl group, or a two-seat ligand with partially hydrogenated group thereof being bonded via the lower alkylene group, and the ligand L2 being the hydrocarbon group having 1 to 12 carbon atoms, alkoxy group, aryloxy group, halogen atom, trialkylsilyl group or hydrogen atom; and
x represents the valence of the transition metal atom M.)
Specific examples of the transition metal compound represented by the general formula (II) include the following compounds:
Ethylenebis(indenyl)zirconiumdichloride;
Ethylenebis(4-methyl-1-indenyl)zirconiumdichloride; and
Ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconiumdichloride.
It is desirable that a combination of at least one transition metal compound selected from among the transition metal compounds represented by the general formula (I) and at least one transition metal compound selected from among the transition metal compounds represented by the general formula (II) should be used for the transition metal compound. In the case of using such combination, the (I)/(II) mol ratio is in the range of preferably 99/1 to 50/50, more preferably 97/3 to 70/30, much more preferably 95/5 to 75/25.
 less than (b) Organoaluminium Oxy-compound greater than 
The organoaluminium oxy-compound may be the benzene-soluble organoaluminium oxy-compound already known to the public or the benzene-insoluble organoaluminium oxy-compound disclosed in Japanese Laid-Open Patent Publication No. 276807/1990. The organoaluminium oxy-compound may be used singly or in combination of not less than two types.
Such organoaluminium oxy-compound may be prepared by the following method, for example:
(1) Method in which an organoaluminium compound such as trialkylaluminium is added to a hydrocarbon medium suspension of magnesium chloride hydrate, copper sulfate hydrate, aluminium sulfate hydrate, nickel sulfate hydrate, cerium chloride hydrate, etc. to allow them to react with each other so that an organoaluminium oxy-compound may be recovered as hydrocarbon solution;
(2) Method in which water, ice or steam is added directly to organoaluminium compound such as trialkylaluminium in a solvent such as benzene, toluene, ethyl ether and tetrahydrofuran to allow them to react with each other, so that an organoaluminium oxy-compound may be recovered as hydrocarbon solution; and
(3) Method in which an organic tin oxide such as dimethyltinoxide or dibutyltinoxide is added to an organoaluminium compound such as trialkylaluminium in a solvent such as decane, benzene and toluene.
Specific examples of the organoaluminium compound used in preparing the aluminiumoxy compound include the following compounds:
(1) Trialkylaluminiums such as trimethylaluminium, triethylaluminium, tripropylaluminium, triisopropylaluminium, tri-n-butylaluminium, triisobutylaluminium, tri-sec-butylaluminium, tri-tert-butylaluminium, tripentylaluminium, trihexylaluminium, trioctylaluminium and tridecylaluminium;
(2) Tricycloalkylaluminiums such as tricyclohexylaluminium and tricyclooctylaluminium;
(3) Dialkylaluminiumhalides such as dimethylaluminiumchloride, diethylaluminiumchloride, diethylaluminiumbromide and diisobutylaluminiumchloride;
(4) Dialkylaluminiumhalides such as diethylaluminiumhalide and diisobutylaluminiumhalide;
(5) Dialkylaluminiumalkoxides such as dimethylaluminiummethoxide and diethylaluminiumethoxide; and
(6) Dialkylaluminiumaryloxides such as diethylaluminiumphenoxide.
Out of these, especially the use of trialkylaluminium is preferablely used.
Furthermore, as this organoaluminium compound, isoprenylaluminium represented by the following general formula may be used:
(i-C4H9)xAly(C5H10)z
(In the above formula, x, y and z are positive numbers, and zxe2x89xa62x.)
Examples of the solvent used in preparing the aluminium oxy-compound include aromatic hydrocarbons such as benzene, toluene, xylene, cumene and cymene, aliphatic hydrocarbons such as pentane, hexane, heptane, octane, decane, dodecane, hexadecane and octadecane, alicyclic hydrocarbons such as cyclopentane, cyclohexane, cyclooctane and methylcyclopentane, petroleum fractions such as gasoline, kerosine and gas oil, and halides, especially chlorides and bromides, of the aforesaid aromatic hydrocarbons, aliphatic hydrocarbons and alicyclic hydrocarbons, particularly hydrocarbon solvents. In addition, ethers such as ethylether and tetrahydrofuran may be used. Out of these solvents, especially aromatic hydrocarbons are preferable.
Here, the benzene-insoluble organoaluminium oxy-compounds contain not more than 10%, preferably not more than 5% of the Al component soluble in benzene at 60xc2x0 C. as converted into Al atoms, and are insoluble, or do not dissolve readily, in benzene.
 less than (c) Support greater than 
The support to be used is an inorganic or organic compound, which is a solid in the state of granules or fine particles having the particle diameter of 10 to 300 xcexcm, preferably 20 to 200 xcexcm. Such inorganic support is preferably a porous oxide, and specific examples of the inorganic support include SiO2, Al2O3, MgO, ZrO2, TiO2, Sb2O, CaO, ZnO, BaO and ThO2, or mixtures of these, such as SiO2xe2x80x94MgO, SiO2xe2x80x94Al2O3, SiO2xe2x80x94TiO2, SiO2xe2x80x94V2O5, SiO2xe2x80x94Cr2O3 and SiO2xe2x80x94TiO2xe2x80x94MgO. Out of these, oxides comprising SiO2 or Al2O3 as the principal component are preferable.
Such support differs in properties, depending on the kind and the manufacturing process thereof. However, the support preferably to be used has preferably a specific surface of 50 to 1,000 m2/g, preferably 100 to 700 m2/g, and a pore volume of 0.3 to 2.5 cm3/g. The support may be sintered as required at 100 to 1,000xc2x0 C., preferably 150 to 700xc2x0 C. before use.
As an example of other supports that can be used, a granular or fine-particle solid of an organic compound having a particle diameter of 10 to 300 xcexcm may be cited. Examples of such organic compound include polymers or copolymers comprising xcex1-olefins having 2 to 14 carbon atoms, such as ethylene, propylene, 1-butene and 4-methyl-1-pentene as the principal component, or polymers or copolymers comprising vinylcyclohexane and styrene as the principal component.
 less than (d) Organoaluminium Compound greater than 
For the organoaluminium compound that is to be added as required, the compound represented by the following general formula (III) may be cited as an example:
R1(n)Al X(3xe2x88x92n)xe2x80x83xe2x80x83(III)
(In the above formula,
R1 represents the hydrocarbon group having 1 to 12 carbon atoms,
X represents halogen atom or hydrogen atom, and
n is 1 to 3.)
Examples of R1 include the alkyl group, cycloalkyl group or aryl group, specifically methyl group, ethyl group, n-propyl group, isopropyl group, isobutyl group, pentyl group, hexyl group, octyl group, cyclopentyl group, cyclohexyl group, phenyl group and tolyl group.
As specific examples of such organoaluminium compound, the following compounds may be cited:
(1) Trialkylaluminiums such as trimethylaluminium, triethylaluminium, triisopropylaluminium, triisobutylaluminium, trioctylaluminium and tri-2-ethylhexylaluminium;
(2) Alkenylaluminiums such as isoprenylaluminium;
(3) Dialkylaluminiumhalides such as dimethylaluminiumchloride, diethylaluminiumchloride, diisopropylaluminiumchloride, diisobutylaluminiumchloride and dimethylaluminiumbromide;
(4) Alkylaluminiumsesquihalides such as methylaluminiumsesquichloride, ethylaluminiumsesquichloride, isopropylaluminiumsesquichloride, butylaluminiumsesquichloride and ethylaluminiumsesquibromide;
(5) Alkylaluminiumdihalides such as methylaluminiumdichloride, ethylaluminiumdichloride, isopropylaluminiumdichloride and ethylaluminiumdibromide; and
(6) Alkylaluminiumhidrides such as diethylaluminiumhidride and diisobutylaluminiumhidride.
Furthermore, as this organoaluminium compound, the compound represented by the following general formula (IV) may be used:
R1(n)Al Y(3xe2x88x92n)xe2x80x83xe2x80x83(IV)
(In the above formula,
R1 represents the same hydrocarbon group as R1 of the aforesaid
general formula (III);
Y represents the xe2x80x94OR2 group, xe2x80x94OSi(R3)3, OAl(R4)2 group, xe2x80x94N(R5)2 group, xe2x80x94Si(R6)3 group or xe2x80x94N(R7)Al(R8)2 group; n is 1 to 2; R2, R3, R4 and R8 represent the methyl group, ethyl group, isopropyl group, isobutyl group, cyclohexyl group, phenyl group, etc.; R5 represents hydrogen atom, methyl group, ethyl group, isopropyl group, phenyl group, trimethylsilyl group, etc.; and
R6 and R7 represent the methyl group, ethyl group, etc.)
As such organoaluminium compound, the following compounds are specifically used:
(1) Compounds represented by R1(n)Al(OR2)(3xe2x88x92n), such as dimethylaluminium-methoxide, diethylaluminiumethoxide and diisobutylaluminiummethoxide;
(2) Compounds represented by R1(n)Al(OSi(R3)3)(3xe2x88x92n), such as Et2Al(OSiMe3), (iso-Bu)2Al(OSiMe3) and (iso-Bu)2Al(OSiEt3);
(3) Compounds represented by R1(n)Al(OAl(R4)2)(3xe2x88x92n), such as Et2AlOAl Et2 and (iso-Bu)2AlOAl (iso-Bu)2;
(4) Compounds represented by R1(n)Al(N(R5)2)(3xe2x88x92n), such as Me2AlNEt2, Et2Al NHMe, Me2AlNHEt, Et2AlN (SiMe3)2 and (iso-Bu)2AlN(SiMe3)2;
(5) Compounds represented by R1(n)Al(Si(R6)3) such as (iso-Bu)2AlSiMe3; and
(6) Compounds represented by R1(n)Al(N(R7)Al(R8)2)(3xe2x88x92n), such as Et2Al N(Me)AlEt2 and (iso-Bu)2AlN(Et)Al(iso-Bu)2.
Out of the organoaluminium compounds represented by the aforesaid general formulas (III) and (IV), the compounds represented by the general formulas (R1)3Al, R1(n)Al(OR2)(3xe2x88x92n), and R1(n)Al(OAl(R4)2)(3xe2x88x92n). Especially those compounds having the general formula in which R1 is the isoalkyl group and n is 2 are preferable.
 less than Catalyst Preparation Method greater than 
The olefin polymerization catalyst is prepared by bringing component (a), component (b), support (c) and as required component (d) into contact. The sequence of bringing them into contact is selected optionally. However, preferably support (c) and component (b) are mixed and brought into contact, then component (a) is mixed and brought into contact with them, and as required component (d) is mixed and brought into contact.
These components may be brought into contact in an inactive hydrocarbon solvent. Specific examples of such inactive hydrocarbon medium that is to be used in the preparation of the catalyst include aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, octane, decane, dodecane and kerosine; alicyclic hydrocarbons such as cyclopentane, cyclohexane and methylcyclopentane; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as ethylenechloride, chlorobenzene and dichloromethane; and mixtures thereof.
In mixing and bringing into contact component (a), component (b), support (c) and as required component (d), component (a) is used in an amount of normally 5xc3x9710xe2x88x926 to 5xc3x9710xe2x88x924 mol, preferably 10xe2x88x925 to 2xc3x9710xe2x88x924 mol, and the concentration of component (a) is in a range of approximately 10xe2x88x924 to 2xc3x9710xe2x88x922 mol/liter, preferably 2xc3x9710xe2x88x924 to 10xe2x88x922 mol/liter. The atomic ratio (Al/transition metal) between aluminium of component (b) and transition metal of component (a) is normally 10 to 500, preferably 20 to 200. The atomic ratio (Al-d/Al-b) between aluminium atoms (Al-d) of component (d), which is used as required, and aluminium atoms (Al-b) of component (b) is in a range of normally 0.02 to 3, preferably 0.05 to 1.5. The mixing temperature at the time of mixing and bringing into contact component (a), component (b), support (c) and as required component (d) is normally xe2x88x9250 to 150xc2x0 C., preferably xe2x88x9220 to 120xc2x0 C., and the contacting time is normally 1 minute to 50 hours, preferably 10 minutes to 25 hours.
The olefin polymerization catalyst thus obtained is supported in such manner that the transition metal atoms deriving from component (a) are supported in an amount of 5xc3x9710xe2x88x926 to 5xc3x9710xe2x88x924, preferably 10xe2x88x925 to 2xc3x9710xe2x88x924 gram atom per g of support (c). It is desirable that the aluminium atoms deriving from component (b) and component (d) should be supported in an amount of 10xe2x88x923 to 5xc3x9710xe2x88x922, preferably 2xc3x9710xe2x88x923 to 2xc3x9710xe2x88x922 gram atom per g of support (c).
The olefin polymerization catalyst may be a prepolymerized catalyst obtained by prepolymerizing olefin in the presence of component (a), component (b), support (c) and as required component (d). The prepolymerization may be carried out by introducing the olefin into an inactive hydrocarbon solvent in the presence of component (a), component (b), support (c) and as required component (d).
Examples of the olefin that is to be used in the prepolymerization include xcex1-olefins having 2 to 20 carbon atoms, such as ethylene, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene and 1-tetradecene. Out of these, ethylene, or a combination of ethylene and xcex1-olefin that is to be used in the polymerization, is preferable.
At the time of the prepolymerization, component (a) is used in a concentration of normally 10xe2x88x926 to 2xc3x9710xe2x88x922 mol/liter, preferably 5xc3x9710xe2x88x925 to 10xe2x88x922 mol/liter, and the amount of component (a) is used in normally 5xc3x9710xe2x88x926 to 5xc3x9710xe2x88x924 mol, preferably 10xe2x88x925 to 2xc3x9710xe2x88x924 mol per g of support (c). The atomic ratio (Al/transition metal) between aluminium of component (b) and transition metal of component (a) is normally 10 to 500, preferably 20 to 200. The atomic ratio (Al-d/Al-b) between aluminium atoms (Al-d) of component (d), which is used as required, and aluminium atoms (Al-b) of component (b) is in a range of normally 0.02 to 3, preferably 0.05 to 1.5. The prepolymerization temperature is xe2x88x9220 to 80xc2x0 C., preferably 0 to 60xc2x0 C., and the prepolymerization time is 0.5 to 100 hours, preferably 1 to 50 hours.
The prepolymerized catalyst is prepared by the method as described below, for example. Specifically, support (c) is brought into a suspended state in an inactive hydrocarbon. Next, an organoaluminium oxy-compound (component (b)) is added to this suspension and allowed to react for a particular time. After that, the supernatant liquid is removed, and the solid matter thus obtained is brought into a suspended state again in an inactive hydrocarbon. A transition metal compound (component (a)) is added to this system and allowed to react for a particular time. After that, the supernatant liquid is removed, and the solid catalyst component is obtained. Subsequently, the solid catalyst component obtained as described above is added to the inactive hydrocarbon containing the organoaluminium compound (component (d)), and the olefin is introduced into the liquid so that the prepolymerized catalyst is obtained.
It is desirable that the amount of the olefin copolymer formed by the prepolymerization is 0.1 to 500, preferably 0.2 to 300, more preferably 0.5 to 200 g per g of support (c). Further, in the prepolymerized catalyst, component (a) is supported in an amount of approximately 5xc3x9710xe2x88x926 to 5xc3x9710xe2x88x924, preferably 10xe2x88x925 to 2xc3x9710xe2x88x924 gram atom terms of transition metal atoms per g of support (c). It is desirable that the aluminium atoms (Al) deriving from component (b) and component (d) should be supported in a molar ratio (Al/M) to the transition metal atoms (M) deriving from component (a) which ranges from 5 to 200, preferably 10 to 150.
The prepolymerization may be carried out by either batch or continuous process and under either vacuum, normal pressure or raised pressure. It is desirable that in the prepolymerization, a prepolymer is so produced in the presence of hydrogen that at least the intrinsic viscosity [xcex7] as measured in decaline at 135xc2x0 C. is in a range of 0.2 to 7, preferably 0.5 to 5 (dl/g).
 less than Polymerization Method greater than 
The ethylene/xcex1-olefin copolymer (a) used in the invention can be obtained by copolymerizing an ethylene and an xcex1-olefin having 3 to 20 carbon atoms in the presence of the olefin polymerization catalyst or prepolymerized catalyst.
The copolymerization of the ethylene and the xcex1-olefin is conducted in the gas phase or in the slurry-like liquid phase. In slurry polymerization, an inactive hydrocarbon may be used as the solvent, or the olefin itself may be used as the solvent.
Specific examples of the inactive hydrocarbon solvent to be used in such slurry polymerization include aliphatic hydrocarbons such as butane, isobutane, pentane, hexane, octane, decane, dodecane, hexadecane and octadecane; alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane and cyclooctane; aromatic hydrocarbons such as benzene, toluene and xylene; and petroleum fractions such as gasoline, kerosine and gas oil. Out of these inactive hydrocarbon media, the aliphatic hydrocarbons, alicyclic hydrocarbons and petroleum fractions are especially preferable.
In conducting the copolymerization by the slurry polymerization process or the gas phase polymerization process, it is desirable that the aforesaid olefin polymerization catalyst or prepolymerized catalyst should be used in an amount of normally 10xe2x88x928 to 10xe2x88x923, preferably 10xe2x88x927 to 10xe2x88x924 (gram atom/liter) in terms of the concentration of the transition metal atoms in the polymerization reaction system.
Furthermore, in the polymerization, an organoaluminium oxy-compound like component (b) and/or the organoaluminium compound (d) may be added. In this cased, the atomic ratio (Al/M) between the aluminium atoms (Al) deriving from the organaluminium oxy-compound and the organoaluminium compound and the transition metal atoms (M) deriving from the transition metal compound (a) is a range of 5 to 300, preferably 10 to 200, more preferably 15 to 150.
In using the slurry polymerization process, the polymerization temperature is in a range of xe2x88x9250 to 100xc2x0 C., preferably 0 to 90xc2x0 C.; and in using the gas phase polymerization process, the polymerization temperature is in a range of normally 0 to 120xc2x0 C., preferably 20 to 100xc2x0 C.
The polymerization pressure is either normal pressure to a raised level of 100 kg/cm2, preferably 2 to 50 kg/cm2. The polymerization may be accomplished by either batch, semicontinuous or continuous process. The polymerization may also be carried out in two or more stages.
Furthermore, the polymerization may be conducted by carrying out copolymerization in two or more stages in which reaction conditions are different by using one or not less than two reactors.
In the hollow molded article manufacturing method, an ethylene/xcex1-olefin copolymer having the physical properties as described before is fed to a blow-molding machine, sent to the die at the end of an extruder while being melted in the extruder, extruded as a parison from the ring-like die, and blow-molded it in divided blow molds.
At the time of the extrusion of the parison, it is desirable that the molding operations should be performed with the resin pressure controlled as described below as the conditions for extruding the melted material. Specifically, the resin pressure P should be controlled in a range as represented by the following formula that shows a relationship among a resin temperature T (xc2x0 C.), an extrusion rate K (kg/hour), a die-lip cross-section area A (cm2) of the molding machine, and the resin melt flow rate MFR (g/10 minutes):
150xc3x97{K/(MFR)1.5/(Txe2x88x92120)/A}0.2xe2x89xa6Pxe2x89xa6500xc3x97{K/(MFR)1.5/(Txe2x88x92120)/A}0.2.
These molding conditions are desirable extrusion conditions that improve the drawdown characteristic of the parison having the ethylene/xcex1-olefin copolymer layer and enable a hollow molded article having satisfactory appearance to be manufactured at high molding speed.
The container of the invention is a hollow molded article having at least one layer of the ethylene/xcex1-olefin copolymer and being obtained in accordance with the manufacturing method as described before, it may be a single-layer container comprising only the layer of the ethylene/xcex1-olefin copolymer, or a multi-layer container comprising a layer of the ethylene/xcex1-olefin copolymer and a layer of other resin.
The manufacture of the single-layer container is conducted by the common blow-holding method. In manufacturing the multi-layer container, two or more extruders are made available, and a coextrusion die is attached to the end of the section coupling them, and then the manufacture of the container is carried out by the common blow-molding method. Specifically, the ethylene/xcex1-olefin copolymer is extruded from one of the extruders under the desirable extrusion conditions as described before, while another resin is extruded under certain conditions from another extruder, and the extrudates are passed through the coextrusion die to form a multi-layer parison. The parison is sandwiched with a pair of the divided molds and blow-molded so that a multi-layer container is manufactured.
In manufacturing a multi-layer container, a layer of gas barrier resin such as polyamide resin, polyester resin, polycarbonate resin and ethylene/vinyl alcohol copolymer resin may be arranged as another resin layer extruded together with the layer of the ethylene/xcex1-olefin copolymer in a proper manner. Since these gas barrier resin layers do not normally have good adhesion with the ethylene/xcex1-olefin copolymer layer, an adhesive resin layer using unsaturated carboxylic acid graft modified polyolefin or the like is provided between the two layers.
Depending on the kind of the contents of the container or the physical properties required of the container itself, a three layer structure comprising the ethylene/xcex1-olefin copolymer layer/adhesive resin layer/gas barrier resin layer may be used, or a more than three layer structure having four or five layers, which include another resin layer provided between the aforesaid layers or outside the gas barrier resin layer, may be used.
Such single-layer or multi-layer containers may be used as packaging containers such as general purpose containers, kerosene cans, industrial chemicals cans, gasoline tanks, mayonnaise containers, ketchup containers, edible oil bottle, bag-in-boxes and drum-inner-bags and as blow-molded tubes for storing wasabi Japanese horseradish paste, mustard paste, etc.